The invention relates to a micro-switch operated web or sheet feeding apparatus, and is of particular application in reprographic apparatus in which the passage of web or sheet material through a feeding apparatus is to be monitored by one or more micro-switches.
In a diazo copying machine in which a master sheet to be copied is passed through a feeding apparatus into overlying abutment with a sheet of photo-sensitive paper, and the passage of the master sheet is monitored so as to initiate the feed of this photo-sensitive paper, or to cut the trailing edge of the photo-sensitive paper, two sets of endless bands are respectively trained around co-operating pairs of driven and driving rollers so that the opposed reaches of the band in each set move in the same direction and define a passageway for conveying the master sheet. To monitor the passage of the master sheet, photocells are often used. These are arranged so that a beam of light from a light source passes through the gap between adjacent bands of the first and second sets so as to impinge upon a light sensor whenever there is no master sheet disposed in the beam of light. However, this arrangement suffers from the disadvantages that:
A. THE MATERIALS PASSING THROUGH THE PASSAGEWAY DEFINED BY THE BANDS ARE THEMSELVES OF VARYING TRANSLUCENCE,
B. THERE IS INTENSE LIGHT ALREADY COMING IN FROM LAMPS IN THE MACHINE. Thus, the photocells have to be adjusted to a high degree of sensitivity and this tends to make sensing unreliable.
In an alternative arrangement, for more positive operation, micro-switches are arranged so that their actuating members are disposed in gaps between adjacent bands of the two sets of endless bands so as to extend across the passageway for the master sheet. However, in view of the close spacing between the adjacent bands in each set, it is quite possible for the micro-switch to be actuated by engagement of the actuating member of the micro-switch by one of the edges of the adjacent bands. Moreover, when the actuating member has been deflected due to the passage of a master sheet through the passageway between the opposed reaches of the band, it is quite common for the actuating member to be displaced laterally so that when the master sheet has passed below the micro-switch the actuating member comes to rest on top of one of the bands adjacent the micro-switch.